INTRASPECIFIC INTERACTIONS AND FEEDING BIOLOGY OF THE DEPOSIT FEEDER, SCOLOPLOS FRAGILIS (VERRILL, 1873) (ORBINIDAE: POLYCHAETA)

How intra- and interspecific interactions among deposit feeding organisms affect the feeding biology of these organisms is only partially understood. Yet, if interactions are important to feeding biology of deposit feeders, then the impact of such interactions must be considered in detritus food chain models. The purpose of this dissertation was to study the feeding biology of the burrowing, sedimentary deposit-feeder Scoloplos fragilis (Verrill, 1873), with emphasis on the influence of intraspecific interactions on sediment reworking (= defecation) rates, emigration behavior and ingestion rates.;Sediment reworking (= defecation) rates varied nonlinearly with changes in density of S. fragilis. As density increases S. fragilis emigrates from the sediments with increasing frequency. Reworking rates are equivalent to those of other polychaete species of similar size. Traditional schemes of mobility modes in marine, benthic invertebrates must be modified to include organisms that spend time in the water column. A method, developed to measure influence of changes in density of S. fragilis on its ingestion rate, entails marking the sediments with a ('14)C label and feeding them to S. fragilis. While ingestion rate decreases with increases in density, these differences are not statistically significant because S. fragilis feed at variable rates.;S. fragilis ingests particulate material with its sac-like, lobate, ciliated, mucus-covered proboscis, that leads to the straight, ciliated digestive tract consisting of the esophagus, stomach, intestine, and anus. S. fragilis ingests a higher percentage of particles 0.2 mm in diameter and a lower percentage of particles 0.1-0.2 mm in diameter than were available in field sediments. When held in seawater, S. fragilis clears its gut of sediments in three hours and when returned to sediments, S. fragilis fills its gut within an hour. When S. fragilis feeds on small (23 um) and large (200-350) particles simultaneously after the gut has cleared, small particles move a greater distance down the digestive tract than large ones. This difference is not always statistically different.